A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. For example, various physical or cognitive functions are directed or affected by neural activity within the various regions of the cerebral cortex. For most individuals, particular areas of the brain appear to have distinct functions. In the majority of people, for example, the areas of the occipital lobes relate to vision; the regions of the left inferior frontal lobes relate to language; portions of the cerebral cortex appear to be involved with conscious awareness, memory, and intellect; and particular regions of the cerebral cortex as well as the basal ganglia, the thalamus, and the motor cortex cooperatively interact to facilitate motor function control.
Aphasias are neurological disorders that affect the language centers of the brain. Aphasias are typically caused by brain lesions that result from a stroke or head injury. Different aphasias result from damage to different portions of the brain's language centers. For example, Broca's aphasia typically results from a large frontal lobe lesion and causes the patient to speak with great effort in a nonfluent manner, while generally not affecting the patient's comprehension of single words and simple sentences. Wernicke's aphasia typically results from damage to the left temporal lobe of the brain and impacts the patient's comprehension of words and sentences, usually without affecting the patient's fluency. Global aphasia can affect both Broca's area and Wernicke's area of the brain and can accordingly adversely affect both the patient's comprehension and speech fluency. Conduction aphasia is caused by damage to structures that interact with the major language areas of the brain. Conduction aphasia does not have as substantial an effect on the patient's comprehension or fluency as do other aphasias, but reduces the patient's ability to repeat sentences verbatim or easily name pictures and objects.
Practitioners have developed imaging techniques to isolate the portions of the brain affected by various aphasias. For example, Perani, et al. disclose identifying and tracking neurological functioning connected with language-based activities by obtaining functional magnetic resonance imaging (fMRI) data while the patient executes language-based tasks (see “A fMRI Study of Word Retrieval in Aphasia,” Brain and Language 85 (2003) pp. 357-368). Practitioners have also treated aphasia, for example, with conventional and/or melodic speech therapies, with drugs (e.g., amphetamines and other neuro-stimulatory agents) and with transcutaneous magnetic stimulation (TMS) applied to the brain. However, these techniques all suffer from drawbacks. In particular, the efficacies of speech therapy and drug-based techniques have not been conclusively demonstrated, and the effects of TMS are short-lived.